1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer, and more particularly to a polishing apparatus having a cloth cartridge which is detachably exchangeably mounted on a turntable.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnections is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 .mu.m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus, and such a process is called Chemical Mechanical Polishing (CMP) in which the semiconductor wafers are chemically and mechanically polished while supplying an abrasive liquid comprising abrasive grains and chemical solution such as alkaline solution.
Conventionally, a polishing apparatus has a turntable and a top ring which rotate at respective individual speeds. A polishing cloth is attached to the upper surface of an turntable. A semiconductor wafer to be polished is placed on the polishing cloth and clamped between the top ring and the turntable. An abrasive liquid containing abrasive grains is supplied onto the polishing cloth and retained on the polishing cloth. During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the polishing cloth is therefore polished by a combination of chemical polishing and mechanical polishing to a flat mirror finish while the top ring and the turntable are rotated.
After, for example, one or more semiconductor wafers have been polished, the polishing cloth is processed to recover its original polishing capability. Various processes have been and are being developed for restoring the polishing cloth, and are collectively called "dressing". The polishing cloth is dressed by a dressing tool in order to enable the polishing apparatus to perform a good polishing function at all times without undesired degradation of polishing performance.
That is, a number of polishing processes are performed on the polishing cloth and a number of dressing processes are applied to the dressing cloth and thus cause the polishing cloth to be worn down, and hence the polishing cloth has to be replaced with a new one periodically. When replacing the polishing cloth, the polishing apparatus is shut down, and the polishing cloth is detached from the turntable. Thereafter, abrasive liquid remaining on the turntable is washed out, and a new polishing cloth is attached to the turntable after drying the turntable. This maintenance operation is troublesome and requires a long period of time during which the polishing apparatus continues to be shut down, thus lowering the productivity of the semiconductor devices per unit time.
In order to solve the above problems, there has been proposed a cloth cartridge which is detachably exchangeably mounted on the turntable. When a polishing cloth is worn down and required to be replaced, the cloth cartridge which has a polishing cloth mounted on a base plate and can be easily detached from the turntable is replaced with a new one which can be easily mounted on the turntable. Thus, the time required for replacement of the polishing cloth is relatively short, and the time that the polishing apparatus apparatus is shut down can be shortened to thus increase the productivity of the semiconductor devices per unit time.
However, the conventional cloth cartridge has a relatively large outer diameter and is difficult to handle. To be more specific, the cloth cartridge normally has a diameter of 600 mm or more, and hence the replacement of the cloth cartridge involves removal of a disk-shaped object having a diameter of 600 mm or more from the polishing apparatus. In many cases, the polishing apparatus is installed in a clean room, an(i when the cloth cartridge is replaced, the polishing cloth is normally wet with an abrasive liquid and such condition of the polishing cloth is not suitable for the environment of the clean room. In order to prevent the cloth cartridge from being exposed to the environment of the clean room, the cloth cartridge is packed in a bag or wrapped by a sheet inside the polishing apparatus, and then the packed or wrapped cloth cartridge is taken out from the polishing apparatus. In this case, since the cloth cartridge has a large diameter and the operation of replacement of the cloth cartridge has to be performed in a narrow space in the polishing apparatus, handling of the cloth cartridge is troublesome and the replacement operation is time-consuming.